(none) when content is '0'

When the value of a ReadonlyField is set to '0', it shows up as '(none)' in the form.
This is because in FormField.php, the Field function starts like this:
function Field() {
if($this->value) ...
I changed it to
if(isset($this->value))
to get it to work.

This seems systemic in *Field.php; I saw it everywhere '(none)' was being generated.
Is this a bug or the desired behavior?

[I've just been using SilverStripe/Sapphire for a month now, and I love it! Even the unusual things I've tried that were painful to get working in Drupal fit right in to your system. Thanks so very much! I hope I will have modules to contribute back.]